There are a few common misconceptions about fertile eggs that will be cleared up in this article, but first, it is important to understand the differences between fertile and infertile eggs as well as incubated and un-incubated fertile eggs.
A hen must mate with a rooster in order for her egg to contain both the male and female genetic material necessary to create an embryo inside the egg. An infertile egg contains only the hen’s genetic material, which means a chick can never hatch from that egg. The hen’s genetic material, termed the blastodisc, can be identified on infertile eggs as a light-colored dot with irregular borders. Every egg contains a blastodisc.
When an egg is fertilized by a rooster, the blastodisc becomes known as the blastoderm, which is the first stage of embryonic development. The blastoderm is identified by its bullseye appearance, having regular, concentric circles. The blastodisc will remain in a state of suspended animation, so to speak, forever unless warmed at particular temperatures for several hours. When a fertile egg is incubated under precise, steady temperatures and humidity levels for 21 days, the blastoderm may develop into a chick.
INCUBATED FERTILE EGG
A fertile egg must be kept at a temperature of at least 85°F for several hours in order for the blastodisc to begin developing into an embryo.
UN-INCUBATED FERTILE EGG
A fertile egg that is never incubated will never contain an embryo and will never look like anything other than common breakfast food.
MYTHS & FACTS ABOUT FERTILE EGGS
MYTH: A fertile egg has a baby chick in it.
FACT: Freshly laid eggs can never contain a chick. Only fertile eggs that have been incubated under proper conditions can become an embryo and develop into a chick. To see exactly how an embryo develops, from the inside and out, each of the 21 days until it hatches, visit my blog here.
MYTH: Fertile eggs are more nutritious than infertile eggs.
FACT: There is no scientific evidence that fertile eggs are nutritionally superior to infertile ones. Fertile eggs have remnants of the male’s sperm and a small layer of cells that could form the embryo. The proportion of these to the total egg is so small that it is impossible to detect chemical differences between fertile and infertile eggs.1
There is no scientific evidence that fertile eggs are nutritionally superior to infertile ones. Fertile eggs have remnants of the male’s sperm and a small layer of cells that could form the embryo. The proportion of these to the total egg is so small that it is impossible to detect chemical differences between fertile and infertile eggs.
MYTH: Fertile eggs taste different from infertile eggs.
FACT: There is absolutely no flavor difference between fertile and infertile eggs.
MYTH: A blood spot inside the egg means the egg is fertile.
FACT: A blood spot inside an egg can occur at various points in a hen’s reproductive system as a result of a blood vessel rupturing. It can be the result of a genetic predisposition, a vitamin A deficiency, or a random event. There is no correlation between blood spots and fertile eggs. The misconception may have come about due to the appearance of incubated, fertile eggs developing veins at or around day four into incubation. Veining looks nothing like a blood spot, however.
The blood in the following photo of an unincubated egg is NOT a developing embryo. The blood has nothing to do with the egg being fertilized or not fertilized, it was caused by a glitch that occurred while the yolk was being released from the hen’s ovary and would have occurred whether or not a rooster mated with the hen that laid this egg.
MYTH: Candling an egg will reveal whether the egg is fertile or not. (Candling is the term used for shining a light through an eggshell to see what’s inside.)
FACT: Only eggs that are incubated and begin developing can be identified as fertile after a minimum of 3 days. The blastoderm and blastodisc cannot be seen through the shell. It is possible for an incubated egg to be fertile and appear infertile when candled if the egg failed to develop. The only way to determine whether an unincubated egg is fertile is to crack it open and identify the blastodisc or blastoderm.
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